Trypanosoma cruzi is the causal agent of Chagas' disease, a long lasting, incapacitating and often lethal disease. Approximately 18 million people in Central and South America are infected with this parasite. Although the autochthonous infection in the US is very rare, several cases have been reported occurring as a consequence of blood transfusion or organ transplantation. More over, recent studies have pointed out that 2% (Los Angeles) to 5% (Washington, DC) of the hispanics living in the US are infected. Not only these people may contribute to spreading the disease, but also they are likely to suffer complications therefore contributing to increases in health cost. Currently, there are no drugs available to treat the chronic form of this disease, even though several target targets is the enzyme NADH-fumarate reductase which is present in all stages during the life cycle of T. cruzi but is not present in mammalian cells. In the last few years we have investigated the role of this enzyme utilizing T. brucei procyclic trypomastigotes as a non infective model. We have purified the enzyme, studied its subcellular localization and identified powerful inhibitors that not only block the enzyme in vitro but also inhibit T. brucei procyclic trypomastigotes growth in culture. Several of these inhibitors block the enzyme NADH-fumarate reductase of T. cruzi epimastigotes. We propose to evaluate whether this enzyme constitutes a suitable target to develop an effective chemotherapy against Chagas' disease. The specific aims of this project include: 1) Purification of the enzyme NADH-fumarate reductase from T. cruzi epimastigotes to test inhibitors and determine their potency; 2) evaluation of efficacy of fumarate reductase inhibitors (four of them synthesized in our laboratory and two commercially available) on T. cruzi epimastigotes, trypomastigotes and amastigotes (grown in mammalian cells); 3) Determination of changes in the intracellular concentration of metabolic intermediates (i.e., succinate, fumarate, ATP and NADH) caused by fumarate reductase inhibitors. These experiments will provide important information regarding the enzyme NADH-fumarate reductase as a target against Chagas' disease.